Modern drug discovery dates back to Alexander Fleming's confirmation of penicillin as an antibacterial agent in 1928. For the last 8 decades, many effective antibiotics have been identified and commercialized. However, bacteria have lived on the Earth for billions of years and have survived a wide range of naturally occurring antibiotics. Their resistance to antibiotics discovered by humans is therefore not surprising. In 2004, over 70% of pathogenic bacteria had generated resistance to at least one commercially available antibiotic. In addition, many evolving pathogens have caused new diseases. There is therefore a demand for new antibiotics that are active against resistant bacteria.